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A Tiny Menace Island-Hops
the Caribbean

This low-temperature scanning electron micrograph shows that
the red palm mite uses its stylets to feed deeper into leaf tissue than most
plant-feeding mites do. This menacing mite is spreading quickly in the
Caribbean and causes serious damage to palms. (Magnified about 3,000x.)(D799-1)

USDA scientists have joined a
multinational effort to stop a tiny mite that may create big problems in and
near this hemisphere’s Tropics.

Researchers at the Department’s
Agricultural Research
Service (ARS) and at the Animal and Plant Health Inspection Service
(APHIS)—are targeting the red palm mite, Raoiella indica. This
pest rides the wind and was known for attacking coconut palms in the Eastern
Hemisphere’s tropical and subtropical regions.

“That’s changed now,” says entomologist
Ronald Ochoa, a world-renowned mite expert at ARS’s Systematic Entomology
Laboratory (SEL). “The red palm mite has been found in the Caribbean
region—in St. Lucia, Dominica, Guadeloupe, Martinique, St. Martin, the
Dominican Republic, and Trinidad. And very recently, it was reported for the
first time on U.S. soil, in Puerto Rico and in St. Thomas.

“It’s spreading quickly and in great numbers.
In fact, this invasion represents the biggest mite explosion ever observed in
the Americas.”

Ochoa explains that R. indica, which was first
described in India in 1924, is a significant pest in the Philippines,
Mauritius, and Egypt. It’s also been spotted in Pakistan, Israel, and
Sudan. “It causes serious leaf damage, ruining the ornamental value of
palms,” says Ochoa. “A grower in Trinidad indicated that he
anticipates a 50-percent loss in coconut production on his property.”

The discolored areas on the underside of this banana leaf are
where red palm mites have caused damage to the plant.
(D798-3)

First identified in the Western Hemisphere 3 years ago on
Martinique, the mite’s calling cards include yellow spots or totally
discolored palm leaves as well as reddish-brown areas indicating mite clusters.

Ochoa and fellow SEL entomologist Ethan Kane were amazed
by the sheer numbers of mites they saw during visits to affected islands.
“I’ve never seen anything like it,” says Ochoa. “In
Trinidad, we estimated there were 30 to 100 million mites per
palm!”

Troubling Observations

Ochoa and Kane have seen other ominous signs. “For
one, it has spread to other exotic and ornamental palms,” says Ochoa.
“And on Dominica, it’s attacking banana plants. In Trinidad, it was
observed on Heliconia. Overall, we’re talking about a
potentially devastating economic impact.”

Another worrisome aspect is the mite’s ability to
disperse via the wind.

The red palm mite, Raoiella indica, an invasive
species in the Caribbean, may threaten several important palms found in the
southern United States. (D799-2)

“There’s no question that hurricanes or human
activity will eventually spread R. indica to tropical and subtropical
regions throughout the Americas,” says Ochoa. The palm trees that are
symbolic of tropical climes, as well as the multimillion-dollar palm-nursery
industry, are at risk.

Scientists have gained some traction against the red palm
mite, thanks in great measure to the observations and actions of local
authorities in the affected Caribbean countries.

In 2004, officials with St. Lucia’s Ministry of
Agriculture, Forestry, and Fisheries noticed an arthropod they suspected of
inducing lethal yellowing disease on coconut palms. They sent samples in
alcohol to SEL’s research facility in Beltsville, Maryland, where Ochoa
and Kane identified the pest as R. indica. Later, they looked at live
specimens with Eric Erbe, a botanist at the Electron Microscopy Unit of
ARS’s Soybean Genomics Laboratory, also in Beltsville. There, the mite
was studied using low-temperature scanning electron microscopy (LTSEM).

“This technology,” says Kane, “provides
an unparalleled ability to explore not only the physical features of the mite,
but also the manner in which it interacts with its environment. Amazingly, this
marked the first time that the red palm mite had been studied to this extent.

“We found that the red palm mite appears to feed on
tissue layers deep within the leaves. It doesn’t feed on the epidermal
cells, as some plant-feeding mites do, but likely on the mesophyll tissues of
the leaf. The implications of this type of feeding are clearly reflected in the
symptoms shown by infested plants.”

A low-temperature scanning electron microscope was used to
produce these detailed images of the red palm mite, Raoiella indica.
Entomologists Ronald Ochoa (right) and Ethan Kane (middle) and botanist Eric
Erbe study the images to learn about the mite’s feeding habits.
(D797-1)

With Help Comes Hope

Ultimately, officials in St. Lucia and with
Dominica’s Department of Agriculture were brought into the effort to find
solutions to help control and contain the mite, as was APHIS’s Caribbean
Area Safeguarding Program. APHIS is funding the ongoing studies.

Also contacted were two more ARS facilities in Beltsville.

At the Bee Research Laboratory, entomologist Jay Evans
isolated and sequenced a piece of the red palm mite’s DNA. “This is
useful because we can collect potential predators and look for red palm mite
DNA in their gut,” says Ochoa. “Then we know they’re eating
them.”

Finding natural predators of the mite has proven to be a
challenge. “For each predator we find on a particular plant, we see 40 to
400 red palm mites,” says Ochoa. “There’s no way the
predators can eat them all.”

Coconut palm trees. (D798-4)

There may be hope in studies focusing on lacewings being
conducted at ARS’s Chemicals Affecting Insect Behavior Laboratory. It is
there that chemist Kamal Chauhan isolated a catnip-oil compound that attracts
lacewings of the insect family Chrysopidae.

“Lacewings are a good predator of soft-bodied
bugs,” says Chauhan. “The challenge is getting them to stick around
and do the job.”

Once researchers define which lacewing species are endemic
to the areas at risk in the Caribbean, Chauhan plans to explore whether the
technologies he developed could be used to entice those local predators to
congregate and help in the efforts to control the red palm mite.

Looking ahead, Kane says the data gathered from the LTSEM
study will help researchers solve taxonomic and systematic challenges in
identifying the mite in other places.

And officials in Puerto Rico, St. Lucia, and
Trinidad—along with scientists Jorge Pena and Marjorie Hoy at the
University of Florida, Jose Carlos Rodrigues at the University of Puerto Rico,
Cal Welbourn at the Florida Department of Agriculture’s Division of Plant
Industry, and APHIS’s Amy Roda—will study further chemical and
cultural control of the mite and monitor for new hosts.

“Also, it’s vital that the affected Caribbean
islands be surveyed as soon as possible for this mite, beginning in Trinidad,
where it’s out of control,” says Ochoa. “Equally important
will be alerting officials in other Caribbean nations and in Florida about what
we have learned.”

“Already, the cooperation between the USDA agencies
and Caribbean nations has proven fruitful,” adds Russell A. Duncan, head
of the APHIS Caribbean Area Safeguarding Program. “Those countries
alerted us, giving both ARS and APHIS the chance to help solve the red palm
mite problem and to conduct research that will help mitigate risks of a U.S.
incursion.

“It’s a great example of how a very effective
pest-control strategy can begin.”—By Luis Pons and Rosalie Marion
Bliss, Agricultural Research Service Information Staff.

This research is part of Plant Diseases (#303) and Crop
Protection and Quarantine (#304), two ARS National Programs described on the
World Wide Web at www.nps.ars.usda.gov.